Optical recording medium and its manufacturing method

ABSTRACT

An optical recording medium capable of suppressing film thickness irregularity of interlayer between a plurality of optical recording layers and effects of warps of a transfer substrate and arising of dusts and burrs problems, etc. and a method of producing the optical recording medium are provided. An optical recording medium has a structure wherein at least two optical recording layers ( 11, 13 ) stacked via an interlayer  12  and a light transmitting layer  14  provided on the optical recording layer are provided at least one surface of a medium substrate  10 , for performing recording and reproducing by irradiating a light to the optical recording layers ( 11, 13 ) through the light transmitting layer  14 , and the interlayer includes at least one layer of ultraviolet curing resin film made to be a film in advance and is a film formed with an uneven shape corresponding to a recording pit or an uneven shape ( 12   p ) to be a guide groove on its surface and cured.

TECHNICAL FIELD

[0001] The present invention relates to an optical recording medium(hereinafter, also referred to as an optical disk) and particularlyrelates to a multilayer optical disk having a plurality of opticalrecording layers.

BACKGROUND ART

[0002] In recent years, in the information recording field, studies onan optical information recording method have been pursued in variousplaces. This optical information recording method has advantages ofbeing able to record and reproduce in a non-contact way and to becompatible with respective memory formats of a read-only type, arecordable type and a rewritable type, and a wide use range fromindustrial use to consumer use is considered as a method of realizing alarge capacity file at a low cost.

[0003] A large capacity of an optical recording medium (hereinafter,also referred to as an optical disk) for the various optical informationrecording methods as above has been attained by making a spot size on afocal surface small by making a wavelength of a laser light as a lightsource to be used in the optical information recording method short andadopting an objective lens having a large numerical aperture.

[0004] For example, a CD (compact disk) has a laser light wavelength of780 nm, the numerical aperture (NA) of an objective lens of 0.45 and arecording capacity of 650 MB, while a DVD-ROM (digital versatile diskread-only memory) has a laser light wavelength of 650 nm, the NA of 0.6and a recording capacity of 4.7 GB.

[0005] Furthermore, in an optical disk system of the next generation, alarge capacity of 22 GB or more has been studied by attaining a laserlight wavelength of 450 nm or less and the NA of 0.78 or more by usingan optical disk wherein a thin light transmitting protective film (acover layer) of, for example, 100 μm or so is formed on an opticalrecording layer.

[0006] As a method of obtaining a still higher density, a multilayeroptical disk wherein two or more optical recording layers are stacked inthe vertical direction via a physical interlayer has been developed.Below, an optical disk having a plurality of optical recording layers assuch will be also called a multilayer optical disk and an optical diskhaving one optical recording layer will be also called a single layeroptical disk.

[0007] In an optical disk system wherein a laser light wavelength ismade short and the numerical aperture of an objective lens is made largefor attaining a large capacity as above, there are disadvantages thatspherical aberration is liable to occur and a focal depth becomesshallow, etc., and the light transmitting layer is demanded that thefilm thickness does not become out of a predetermined value and a filmthickness irregularity is small.

[0008] In a multilayer disk made by stacking optical recording layers inthe vertical direction, not only the light transmitting layer, but theinterlayer is also demanded to have a predetermined film thickness and asmall irregularity of the film thickness in the same way.

[0009] As a method of forming the interlayer provided between theoptical recording layers, conventionally, a method of forming apredetermined film thickness by spin-coating using an ultraviolet curingresin to secure necessary properties for recording and reproducing hasbeen general.

[0010] However, in the method of forming the interlayer by spin-coatingusing an ultraviolet curing resin as above, there was a disadvantagethat irregularity of the film thickness is liable to occur on inner andouter circumferences of the optical disk and the improvement has beendemanded.

[0011] Furthermore, there have been disadvantages of being susceptibleto the influence of warps of a disk substrate and a transfer substrateand having a weakness for dusts and burrs.

DISCLOSURE OF THE INVENTION

[0012] The present invention was made in consideration of the abovecircumstances and has as an object thereof to provide an opticalrecording medium having a plurality of optical recording layers, capableof suppressing irregularity of a film thickness of an interlayer betweenthe optical recording layers and, moreover, capable of suppressing theinfluence by warps of a transfer substrate and arising of problems dueto dusts and burrs, and a method of producing such an optical recordingmedium.

[0013] To attain the above object, an optical recording medium of thepresent invention has at least two optical recording layers stacked viaan interlayer and a light transmitting layer provided on the opticalrecording layer on at least one surface of a medium substrate and is forperforming recording and reproducing by irradiating a light to theoptical recording layer through the light transmitting layer, whereinthe interlayer includes at least one layer of ultraviolet ray curingresin film made to be a film in advance and is a film formed with anuneven shape corresponding to a recording pit or an uneven shape to be aguide groove on its surface and cured.

[0014] In the optical recording medium of the above present invention,preferably, the interlayer is a film obtained by curing a stackedstructure including at least one layer of ultraviolet ray curing resinfilm made to be a film in advance and at least one layer of a coatingfilm of an ultraviolet ray curing liquid resin composition.

[0015] Furthermore preferably, an uneven shape corresponding to arecording pit or an uneven shape to be a guide groove on the surface ofthe resin film in the interlayer.

[0016] Also furthermore preferably, an uneven shape corresponds to arecording pit or an uneven shape to be a guide groove on the surface ofthe coating film of an ultraviolet ray curing liquid resin composition.

[0017] In the optical recording medium of the above present invention,the interlayer provided between the plurality of optical recordinglayers includes at least one ultraviolet curing resin film made to be afilm in advance and an uneven shape corresponding to a recording pit oran uneven shape to be a guide groove is formed on the surface of theinterlayer.

[0018] The resin film made to be a film in advance has small filmthickness irregularity, and by using this as a part or all of theinterlayer, film thickness irregularity of the interlayer can besuppressed.

[0019] Also, by using a resin film made to be a film in advance, theinfluence of warps of the transfer substrate and arising of problemscaused by dusts and burrs can be also suppressed.

[0020] Also, to attain the above object, a method of producing anoptical recording medium of the present invention is a method ofproducing an optical recording medium having at least two opticalrecording layers, including a step of forming a medium substrate havingan uneven shape on its one surface, a step of forming a first opticalrecording layer on the uneven shape formation surface of the mediumsubstrate, a step of forming an interlayer having an uneven shape on itssurface on the first optical recording layer, a step of forming a secondoptical recording layer on the uneven shape formation surface of theinterlayer, and a step of forming a light transmitting protective layeron the second optical recording layer; wherein the step of forming theinterlayer includes a step of adhering one surface of an ultraviolet raycuring resin film made to be a film in advance to the first opticalrecording layer or a transfer substrate formed with an uneven shape, astep of pressing the transfer substrate or the first optical recordinglayer directly or via other layer against the resin film and providingan uncured interlayer including at least one layer of the resin filmbetween the first optical recording layer and the transfer substrate, astep of curing the interlayer in a state of pressing the transfersubstrate against the surface of the interlayer, and a step of releasingthe transfer substrate from the interlayer and transferring the unevenshape of the transfer substrate to the surface of the interlayer.

[0021] In the method of producing an optical recording medium of theabove present invention, preferably, the resin film is an ultravioletray curing resin film made to be a film in a state of being sandwichedby a pair of release films; and the step of forming the interlayerfurther includes a step of releasing one of the release films from theresin film before the step of adhering the resin film to the firstoptical recording layer or the transfer substrate, and a step ofreleasing the other of the release films from the resin film after thestep of adhering the resin film to the first optical recording layer orthe transfer substrate and before the step of pressing the transfersubstrate or the first optical recording layer directly or via otherlayer against the resin film.

[0022] In the method of producing an optical recording medium of theabove present invention, preferably, the interlayer is formed only withthe resin film in the step of forming the interlayer.

[0023] In the method of producing an optical recording medium of theabove present invention, preferably, the step of forming the interlayerincludes a step of adhering the resin film on the transfer substrate, astep of forming a coating film of an ultraviolet ray curing liquid resincomposition on the first optical recording layer, a step of adhering theresin film and the coating film, a step of obtaining the interlayer byduring the resin film and the coating film in a state of being adheredto each other, and a step of releasing the transfer substrate from theinterlayer.

[0024] Also, in the method of producing an optical recording medium ofthe above present invention, preferably, the step of forming theinterlayer includes a step of forming a coating film of an ultravioletray curing liquid resin composition on the transfer substrate, a step ofadhering the resin film on the first optical recording layer, a step ofadhering the resin film and the coating film, a step of obtaining theinterlayer by curing the resin film and the coating film in a state ofbeing adhered to each other, and a step of releasing the transfersubstrate from the interlayer.

[0025] In the method of producing an optical recording medium of theabove present invention, preferably, one made by an injection moldedplastic material having a larger outer circumference diameter than thatof the medium substrate is used as the transfer substrate.

[0026] In the method of producing an optical recording medium of theabove present invention, preferably, one made by a plastic materialhaving a thickness of 0.5 mm or less is used as the transfer substrate.

[0027] In the method of producing an optical recording medium of theabove present invention, preferably, one made by a plastic materialwherein the outer circumference diameter is taper shaped and thinnerthan the center portion is used as the transfer substrate.

[0028] In the method of producing an optical recording medium of theabove present invention, preferably, adhesion with pressure is performedfrom the transfer substrate side by an elastic body in the step oftransferring by using the transfer substrate.

[0029] In the method of producing an optical recording medium of theabove present invention, at least one layer of ultraviolet curing resinfilm made to be a film is used as an interlayer provided between thefirst and second optical recording layers, and an uneven shapecorresponding to a recording pit or an uneven shape to be a guide grooveis transferred to the surface of the interlayer.

[0030] The resin film made to be a film in advance has small filmthickness irregularity, and by using this as a part or all of theinterlayer, the film thickness irregularity of the interlayer can besuppressed.

[0031] Also, by using a resin film made to be a film in advance, theinfluence of warps of the transfer substrate and arising of problemscaused by dusts and burrs, etc. can be also suppressed.

BRIEF DESCRIPTION OF DRAWINGS

[0032]FIG. 1A is a schematic perspective view showing a state ofirradiating a light on an optical disk according to a first embodimentof the present invention, FIG. 1B is a schematic sectional view and FIG.1C is an enlarged sectional view of a key part of the schematicsectional view in FIG. 1B.

[0033]FIG. 2 is a sectional view showing the configuration of anultraviolet curing resin film.

[0034]FIG. 3 is a schematic view showing the configuration of a devicefor producing an ultraviolet curing resin film.

[0035]FIG. 4A is a schematic view and FIG. 4B is a sectional viewshowing production processes of a method of producing the optical diskaccording to the first embodiment.

[0036]FIG. 5A and FIG. 5B are sectional views showing processescontinued from FIG. 4B.

[0037]FIG. 6A and FIG. 6B are sectional views showing processescontinued from FIG. 5B.

[0038]FIG. 7A and FIG. 7B are sectional views showing processescontinued from FIG. 6B.

[0039]FIG. 8A and FIG. 8B are sectional views showing processescontinued from FIG. 7B.

[0040]FIG. 9A and FIG. 9B are sectional views showing processescontinued from FIG. 8B.

[0041]FIG. 10A and FIG. 10B are sectional views showing processescontinued from FIG. 9B.

[0042]FIG. 11 is a sectional view showing the configuration of anultraviolet curing multilayer resin film wherein two kinds of materialsare stacked.

[0043]FIG. 12 is a sectional view of an optical disk wherein aninterlayer is configured by using a multilayer resin film, particularlyshowing edges of an outer circumference and inner circumference areshown.

[0044]FIG. 13 is a sectional view of an optical disk according to asecond embodiment of the present invention.

[0045]FIG. 14A and FIG. 14B are sectional views showing productionprocesses of a method of producing the optical disk according to thesecond embodiment.

[0046]FIG. 15A and FIG. 15B are sectional views showing. processescontinued from FIG. 14B.

[0047]FIG. 16A and FIG. 16B are sectional views showing processescontinued from FIG. 15B.

[0048]FIG. 17A and FIG. 17B are sectional views showing processescontinued from FIG. 16B.

[0049]FIG. 18A and FIG. 18B are sectional views showing processescontinued from FIG. 17B.

[0050]FIG. 19 is a sectional view of another configuration of theoptical disk according to the second embodiment of the presentinvention.

[0051]FIG. 20A and FIG. 20B are sectional views showing productionprocesses of a method of producing an optical disk having anotherconfiguration according to the second embodiment.

[0052]FIG. 21A and FIG. 21B are sectional views showing processescontinued from FIG. 20B.

[0053]FIG. 22A and FIG. 22B are sectional views showing processescontinued from FIG. 21B.

[0054]FIG. 23 is a partial sectional view showing the schematicconfiguration of a substrate, such as a disk substrate, formed by aninjection molding.

[0055]FIG. 24 is a sectional view showing production processes of amethod of producing an optical disk according to a third embodiment.

[0056]FIG. 25A and FIG. 25B are sectional views of a transfer substrateused in the third embodiment.

[0057]FIG. 26 is a sectional view showing production processes of amethod of producing the optical disk according to the third embodiment.

BEST MODE FOR CARRYING OUT THE INVENTION

[0058] Below, preferred embodiments of the present invention will beexplained in detail with reference to the drawings.

[0059] The present embodiment relates to an optical recording medium(optical disk) and the production method thereof.

[0060] [First Embodiment]

[0061]FIG. 1A is a schematic perspective view showing a state ofirradiating a light on an optical disk provided with two opticalrecording layers according to the present embodiment.

[0062] The optical disk DC has an approximate disk shape having a centerhole CH opened at the center portion and is driven to rotate in thedriving direction DR.

[0063] When recording or reproducing information, the optical recordinglayers in the optical disk DC is irradiated with a light LT, such as alaser light in a blue to blue-violet range, by an objective lens OL, forexample, having the numerical aperture of 0.8 or more.

[0064]FIG. 1B is a schematic sectional view and FIG. 1C is an enlargedsectional view of a key part of the schematic sectional view in FIG. 1B.

[0065] On one surface of a disk substrate 10 made by a polycarbonateresin, etc. having a thickness of 0.3 mm or more (for example, 1.1 mm)is formed a concave portion 10 d. A first optical recording layer 11 isformed along a unevenness including the concave portion 10 d. Aninterlayer 12 is formed thereon, and a convex portion 12 p is providedon the surface of the interlayer 12. A second optical recording layer 13is formed on the interlayer 12 along the unevenness including the convexportion 12 p. A light transmitting protective layer 14, for example,having a film thickness of 0.1 mm is formed thereon.

[0066] The first optical recording layer 11 and the second opticalrecording layer 13 have the configuration of stacking, for example, adielectric film, a recording film of a phase change type recordingmaterial, etc., a dielectric film and a reflection film, etc. from theupper layer side in this order, wherein the configuration and the numberof the layers differ in accordance with a kind and design of therecording material.

[0067] In the case of an optical disk having three or more layers, theconfiguration of the interlayer and the optical recording layer will berepeated.

[0068] In the optical disk as above, the first optical recording layer11 and the second optical recording layer 13 have uneven shapes formedby the concave portion 10 d formed on the surface of the disk substrate10 and the convex portion 12 p formed on the surface of the interlayer12 and are sectionalized to track regions called lands and grooves bythe uneven shapes including the concave portion 10 d and the convexportion 12 p.

[0069] Also, by configuring the optical recording film by a reflectionfilm, such as an aluminum film, by using the uneven shapes formed by theconcave portion 10 d on the disk substrate 10 and the convex portion 12p on the interlayer 12 as a pit having a length corresponding torecording data, a read-only memory (ROM) type optical disk can beobtained.

[0070] When recording or reproducing the above optical disk, a light LT,such as a laser light, is irradiated from the protective film 14 side soas to focus on either of the first optical recording layer 11 and thesecond optical recording layer 13 by adjusting a distance of theobjective lens OL from the optical disk. When reproducing, a returnedlight reflected on either of the first and second optical recordinglayers (11, 13) is received by a flight receiving element and areproducing signal is taken out.

[0071] As explained above, the respective two or more optical recordinglayers are separated by the interlayer in the vertical direction, sothat one of a plurality of the optical recording layers can beselectively recorded or reproduced by changing the focal position.

[0072] In a system of an optical disk having a laser wavelength of 405nm and the NA of 0.85, it is possible to separate between the opticalrecording layers by making the thickness of the interlayer 10 μm ormore.

[0073] Note that when using such a large NA, spherical aberration due tofilm thickness irregularity becomes a problem. The film thicknessirregularity is a total of all light transmittance layers andinterlayer, so that film thickness irregularity of each interlayer isrequired to be as small as possible.

[0074] For example, in a system wherein the laser-wavelength λ is 405 nmand the NA is 0.85, the thickness irregularity is required to be|Δt|<5.26λ/NA⁴, so that the thickness irregularity is required to be ±4μm. Assuming that film thickness irregularity arises to the same extentin the light transmitting layer and interlayer, a multilayer disk havingup to three layers can be configured by suppressing the film thicknessirregularity of the interlayer to ±1 μm.

[0075] The optical disk of the present embodiment is configured that atleast one ultraviolet curing resin film made to be a film in advance isincluded in the interlayer for improving uniformity of the filmthickness of the interlayer 12, and an uneven shape for the secondoptical recording layer is formed on the surface of the interlayer.

[0076] The resin film made to be a film in advance has small filmthickness irregularity, so that the film thickness irregularity of theinterlayer can be suppressed by using it as a part or all of theinterlayer.

[0077] Also, by using the resin film made to be a film in advance, theinfluence of warps of a transfer substrate and arising of a problem ofdusts and burrs can be also suppressed.

[0078]FIG. 2 is a sectional view showing the configuration of the aboveultraviolet curing resin film.

[0079] Release films (12 a and 12 b) are respectively adhered to theupper and lower surfaces of the ultraviolet curing resin film 12 s madeto be a film in advance and released when used.

[0080] As to the release films (12 a and 12 b) on the upper surface andthe lower surface, a force required to release may be differentiated,for example, the release film 12 a on the upper surface may be a heavyreleasability side and the release film 12 b on the lower surface may bethe light releasability side. By differentiating the releasability, itbecomes possible to always release from the light releasability side.

[0081] Since the ultraviolet curing resin film made to be a film inadvance as above has a high viscosity in the resin and does not flow,there is an advantage that processing of stamping out to be a disk shapein advance, etc. becomes possible.

[0082]FIG. 3 is a schematic view showing the configuration of a devicefor producing the above ultraviolet curing resin film.

[0083] An ultraviolet curing resin is in a molten state in a resinsupplying portion SP and mixed to be homogenized. A resin is suppliedfrom the resin supplying portion SP to be applied to the release film 12a fed from a feeding roll Ra in a coating portion CT by a roll coater,knife coater, gravure coater, dye coater and reverse coater, etc., and asolvent is evaporated for those containing solvent in a drying portionDY and those not containing solvent is left as it is to be made to be aresin film 12 s by cooling, etc.

[0084] The other release film 12 b having differentiated releasabilityfed from the feeding roll Rb is adhered on the upper surface of theresin film 12 s and wound by a winding roll Rc.

[0085] As explained above, the resin film 12 s sandwiched by the releasefilms (12 a and 12 b) configured as shown in FIG. 2 can be obtained.

[0086] As the ultraviolet curing resin, those blended with aphotopolymerization monomer, a photopolymerization starting agent and anadditive, or a bind polymer can be used.

[0087] Also, an ultraviolet curing adhesive may be also used, forexample, those composed of a homopolymer and/or a copolymer, such asacrylic acid of an acrylic resin, methyl acrylate, ethyl acrylate,propyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, methacrylicacid, methyl methacrylate, ethyl methacrylate, butyl methacrylate and2-hydroxyethyl acrylate, blended with an ultraviolet curing resin and aphotopolymerization initiator, or those obtained by mixing a polymer anda copolymer of an adhesive, wherein a photo-curing type polymerizinggroup is provided to the side chain, with a photopolymerizationinitiator, etc. may be used. The adhesive is not limited to acrylics andrubbers, silicones, polyvinyl ethers, etc. may be also used.

[0088] Also, an adhesion-providing agent or a filler, softener, wax,antioxidant, cross-linking agent may be blended in accordance with need.

[0089] As the release film, a support sheet wherein at least one surfacehas releasability is sufficient, and the releasability may be given byusing a release treatment agent.

[0090] As a support sheet material, it is preferable to use a plasticfilm having excellent surface smoothness, and plastic films of apolyethylene resin, a polypropylene resin and other polyolefin resins, apolyethylene terephthalate resin, a polybutylene terephthalate resin andother polyester resins, an acetate resin, a polystyrene resin, a vinylchloride resin may be mentioned. As the release treatment agent, asilicone resin, an alkyd resin, a fluorocarbon resin, a cellulose resin,a melamine resin, an acrylic resin, polyurethane resin and a polyesterresin, etc. may be mentioned.

[0091] Next, a method of producing a multilayer optical disk accordingto the present embodiment will be explained with reference to thedrawings.

[0092] First, a disk substrate stamper 20 having on its surface anuneven pattern including a convex portion 20 p as an inverse pattern fortransferring to a disk substrate is prepared by a conventionally knowncertain method.

[0093] Next, as shown in FIG. 4A, the above disk substrate stamper 20 isarranged and fixed inside a cavity composed of molds (MD1 and MD2), sothat a convex portion formed surface 20 p′ of the disk substrate stamper20 faces to inside of the cavity, consequently, an injection moldingmold is configured.

[0094] By injecting a resin 10′, for example, a molten polycarbonateresin, to inside the cavity of the above injection molding mold from aninlet MS of the mold, a disk substrate 10 is formed on the disksubstrate stamper 20 as shown in FIG. 4B.

[0095] Here, on the surface of the disk substrate 10 is formed a concaveportion (groove) 10 d at a position corresponding to the convex portion20 p of the disk substrate stamper 20.

[0096] By releasing from the above injection molding mold, a disksubstrate 10 having an uneven pattern including the concave portion 10 dto be a groove pattern or a pit pattern on its surface as shown in FIG.5A is obtained.

[0097] Next, as shown in FIG. 5B, after removing dusts by blowing a gas,such as an air or a nitrogen gas, to the surface of the disk substrate10, the first optical recording film 11 having a stacked structure of areflection film, a dielectric film, a recording film and a dielectricfilm is formed in this film formation order, for example, by asputtering method, a vacuum evaporation method, spin-coat method, etc.

[0098] As the above recording film, for example, a recording filmincluding a phase change type optical recording film, a magneto-opticalrecording film or an organic dye may be used.

[0099] Alternately, in the case of a ROM type optical disk, the opticalrecording film is formed by a reflection film of an aluminum film, etc.

[0100] When forming a film of a phase change type recording material asthe above recording film, the phase change type recording material iscrystallized by irradiating a YAG laser light or other infrared ray.This corresponds to an initialization process of the first opticalrecording layer 11.

[0101] Next, as shown in FIG. 6A, the release film 12 b on the lightreleasability side of the resin film 12 s sandwiched by the releasefilms (12 a and 12 b) shown in FIG. 2 is released.

[0102] Next, as shown in FIG. 6B, the resin film 12s is adhered to anupper surface of the first optical recording layer 11 by using a pad ora roller, etc.

[0103] After adhering with sufficient strength to obtain the state shownin FIG. 7A, the release film 12 a on the heavy releasability side of theresin film 12 s is released as shown in FIG. 7B.

[0104] Next, as shown in FIG. 8A, a transfer substrate 21, such as aresin stamper, having an uneven pattern including the concave portion 21d for the second optical recording layer formed in a separate process inadvance is adhered to the resin film 12 s by using a pad or a roller,etc.

[0105] By adhering the transfer substrate 21 with a sufficient strength,as shown in FIG. 8B, a convex portion 12 p is transferred at a positioncorresponding to the concave portion 21 d of the transfer substrate 21on the surface of the release film 12 a.

[0106] Next, as shown in FIG. 9A, the resin film 12 s is cured, forexample, by irradiating an ultraviolet ray LW from the transfersubstrate 21 side to obtain an interlayer 12 having an uneven shape forthe second optical recording layer transferred on its surface. Duringthe curing, adhesiveness between the surface of the interlayer 12 andthe transfer substrate 21 declines.

[0107] Next, as shown in FIG. 9B, the surface of the interlayer 12 andthe transfer substrate 21 are separated on the boundary surface.

[0108] Next, as shown in FIG. 10A, after removing dusts by blowing agas, such as an air or a nitrogen gas, to the surface of the interlayer12, the second optical recording film 13 having a stacked structure of atranslucent reflection film, a dielectric film, a recording film and adielectric film is formed in this film formation order, for example, bya sputtering method, a vacuum evaporation method, spin-coat method, etc.

[0109] As the above recording film, for example, a recording filmincluding a phase change type optical recording film, a magneto-opticalrecording film or an organic dye may be used.

[0110] Alternately, in the case of a ROM type optical disk, the opticalrecording film is formed by a translucent reflection film of an aluminumfilm, etc.

[0111] Next, a light transmittance protective layer 14 is formed on thesecond optical recording film 13. The protective layer 14 may be formed,for example, by a method of adhering a protective layer sheet with anadhesive.

[0112] When forming a film of a phase change type recording material asthe above recording film, the phase change type recording material iscrystallized by irradiating a YAG laser light or other infrared ray.This corresponds to an initialization process of the second opticalrecording layer 13.

[0113] From the above, an optical disk having a plurality of opticalrecording layers shown in FIG. 1 can be produced.

[0114] In the above production method, the ultraviolet curing resin filmis adhered to the disk substrate 10 (the first optical recording layer11) side first, but it may be adhered to the transfer substrate 21 sidefirst before bonding with pressure with the disk substrate 10 (the firstoptical recording layer 11).

[0115] As the disk substrate 10, an injection molded substrate using apolycarbonate resin, a PMMA resin, an amorphous polyolefin resin, amodified acrylic resin and other resins and a glass 2P substrate, etc.can be used.

[0116] As explained above, when curing from the transfer substrate 21side, the disk substrate 10 does not always required to have lighttransmittance as far as being provided with an uneven pattern for thefirst optical recording layer.

[0117] As the transfer substrate 21, a Ni stamper may be used, but whenusing a plastic substrate, irradiation of an ultraviolet ray from thetransfer substrate 21 side becomes possible as explained above and itbecomes unnecessary to let an ultraviolet ray pass through to the firstoptical recording layer 11 or to the disk substrate 10. Note that it isnecessary to have a property of being able to be released on theboundary of the transfer substrate 21 and the interlayer 12 after thecuring.

[0118] As a method of obtaining releasability after curing, other then amethod of using a material having low adhesiveness with an ultravioletcuring film, such as a cyclic polyolefin resin, a method of decliningadhesiveness of the ultraviolet curing resin film is possible.

[0119] Specifically, the adhesiveness can be declined by increasingmolecular weight and heightening hardness.

[0120] Note that when the adhesiveness with the disk substrate 10 islost, it can be handled by using at least two kinds of interlayermaterials, using an ultraviolet curing resin film for adhesion at thelowermost portion, and using an ultraviolet curing resin film havinggood releasability from the transfer substrate at the uppermost portion.

[0121] An adhesive force between ultraviolet curing resin films can beobtained by adhering the ultraviolet curing resin films together in anuncured state or in a state only one of them is cured. In this case, notonly the above cyclic polyolefin resin but a general polycarbonateresin, a PMMA resin, a chain polyolefin resin and a modified acrylicresin, etc. can be used.

[0122]FIG. 11 is a sectional view showing the configuration of anultraviolet curing multilayer resin film made by stacking two kinds ofmaterials.

[0123] An ultraviolet curing resin film 12 sa made to be a film inadvance and a resin film 12 sb are stacked, a release film 12 a isadhered to the resin film 12 sa and the release film 12 b is adhered tothe resin film 12 sb, which are released when used.

[0124] The multilayer resin film in this case can be formed in the sameway as the resin film in FIG. 2 by using the device shown in FIG. 3.

[0125]FIG. 12 is a sectional view of an optical disk having a pluralityof optical recording layers, wherein the interlayer is configured byusing the above multilayer resin film, particularly showing edgeportions of an outer circumference and inner circumference.

[0126] The interlayer 12 is a stacked structure of a resin film curedportion 12 sa′ and a resin film cured portion 12 sb′, wherein the firstand second optical recording layers (11 and 13) are not provided at edgeportions of the outer circumference and inner circumference and theinterlayer 12 is configured to directly contact the disk substrate 11and the protective layer 14.

[0127] By selecting two materials for composing the interlayer, theinterlayer 12 can secure adhesiveness with the disk substrate 11 and theprotective layer 14.

[0128] In processes of producing an optical disk having a plurality ofoptical recording layers as above wherein the interlayer is made byusing the above multilayer resin film, when adhering the multilayerresin film first to the disk substrate, the release sheet on the lightreleasability side is made to be on the side of the ultraviolet curingresin film adhered to the disk substrate.

[0129] Also, when adhering the multilayer resin film to the transfersubstrate first, the release sheet on the light releasability side ismade to be on the side of the ultraviolet curing resin film having lowadhesiveness.

[0130] Of course, two or more kinds of ultraviolet curing films may beadhered successively. In this case, they may be adhered either of thedisk substrate side or the transfer substrate side, or separatelyadhered to the both sides and the two may be finally bonded withpressure.

[0131] Advantages obtained by making it multilayer is that hardness,shrinking percentage, transferability, film forming properties andcorrosion behavior can be changed in addition to the above adhesivenessand releasability.

[0132] For example, when hardness is heightened, transferability anddeformation at film formation generally become preferable butadhesiveness declines and shrinking percentage tends to increase. Whenthe shrinking percentage becomes large, there arises a disadvantage ofarising warps on the disk. When it is difficult to satisfy allproperties with one kind of film, for example, by using those havinghigh hardness and good film formation properties as an ultravioletcuring resin film of the upper portion requiring transferability andthose having a small shrinking percentage as an ultraviolet curing resinfilm of the lower portion, an interlayer having good transferabilitywherein warps of a disk is hard to arise can be configured.

[0133] [Second Embodiment]

[0134]FIG. 13 is a sectional view of an optical disk having a pluralityof optical recording layers according to the present embodiment.

[0135] It has substantially the same configuration as that of theoptical disk according to the first embodiment, but has a differentpoint that an interlayer 12 is obtained by adhering an ultravioletcuring resin film made to be a film in advance to a coating film of anultraviolet curing liquid resin composition and curing the same.

[0136] A method of producing the above optical disk will be explained.

[0137] First, a disk substrate 10 is formed in the same way as in thefirst embodiment, a first optical recording film 11 is formed thereon,then, as shown in FIG. 14A, an ultraviolet curing liquid resincomposition 12 r is supplied on the first optical recording film 11, andas shown in FIG. 14B, the liquid resin composition 12 r is applied to bea uniform film thickness to form a coating film by a spin-coat method ofrotating the disk substrate 10.

[0138] Next, as shown in FIG. 15A, the release film 12 b on the lightreleasability side of the resin film 12 s sandwiched by the releasefilms (12 a and 12 b) shown in FIG. 2 is released, and a transfersubstrate 21, such as a resin stamper, having an uneven patternincluding the concave portion 21 d for the second optical recordinglayer formed in a separate process in advance is adhered to the resinfilm 12 s by using a pad or a roller, etc.

[0139] By adhering the transfer substrate 21 with sufficient strength,as shown in FIG. 15B, the convex portion 12 p is transferred to aposition corresponding to the concave portion 21 d of the transfersubstrate 21 on the surface of the release film 12 a.

[0140] Next, as shown in FIG. 16A, the release film 12 a on the heavyreleasable side of the resin film 12 s is released.

[0141] Next, as shown in FIG. 16B, the surface of the coating film ofthe liquid resin composition and the surface of the resin film 12 s areadhered together by using a pad or a roller, etc.

[0142] Next, as shown in FIG. 17A, the resin film 12 s and the coatingfilm of the liquid resin composition 12 r are cured, for example, byirradiating an ultraviolet ray UV from the transfer substrate 21 side soas to obtain an interlayer 12 as a stacked structure of a resin filmcured portion 12 s′ being transferred on its surface the uneven patternfor the second optical recording layer and a liquid resin compositioncoating film cured portion 12 r′. During the curing, adhesiveness of thesurface of the resin film cured portion 12 s′ and the transfer substrate21 declines.

[0143] Next, as shown in FIG. 17B, the surface of the resin film curedportion 12 s′ composing the interlayer 12 and the transfer substrate 21are separated on the boundary.

[0144] After that, in the same way as in the first embodiment, as shownin FIG. 18A, the second optical recording film 13 is formed on the resinfilm cured portion 12 s′ composing the interlayer 12, and a lighttransmitting protective layer 14 is formed thereon.

[0145] From the above, an optical disk having a plurality of opticalrecording layers shown in FIG. 13 can be produced.

[0146] When performing applying by spin-coat by using an ultravioletcuring resin on a shape having a center hole like an optical disk, filmthickness irregularity arises from the inner circumference to the outercircumference of the disk, so that it is difficult to suppress the filmthickness irregularity, for example, to ±1 μm or less with respect tothe thickness of the interlayer of 20 μm.

[0147] In the method of producing in the present embodiment, by making athickness of coating by spin-coat thin to five times as much as the filmthickness irregularity and forming the rest of the thickness with theultraviolet curing resin film, an interlayer having a little thicknessirregularity can be formed.

[0148] For example, when forming an interlayer of 20 μm, by applying aliquid resin of an amount of 5 μm and composing the rest amount of 15 μmwith an ultraviolet curing resin film, total film thickness irregularitycan be suppressed to ±1 μm or less.

[0149] Also, an optical disk according to the present embodiment may bealso configured as shown in FIG. 19.

[0150] The configuration is substantially the same as that of theoptical disk shown in FIG. 13, but in the interlayer 12, an arrangementof the ultraviolet curing resin film made to be a film in advance and acoating film of an ultraviolet curing liquid resin composition isconfigured to be inverse.

[0151] A method of producing the above optical disk will be explained.

[0152] First, an ultraviolet curing liquid resin composition 12 r issupplied on a transfer substrate 21, such as a resin stamper, having anuneven pattern including a concave portion 21 d for a second opticalrecording layer as shown in FIG. 20A, and the liquid resin composition12 r is applied to be a uniform film thickness to form a coating film asshown in FIG. 20B by a spin-coat method of rotating a disk substrate 10.

[0153] Next, the disk substrate 10 is formed in the same way as in thefirst embodiment, after forming a first optical recording film 11thereon, as shown in FIG. 21A, a release film 12 b on the lightreleasability side of a resin film 12 s sandwiched by release films (12a and 12 b) shown in FIG. 2 is released, and the first optical recordingfilm 11 and the resin film 12 s are adhered to each other by using a pador a roller, etc.

[0154] By adhering the transfer substrate 21 with sufficient strength,the state shown in FIG. 21B can be obtained.

[0155] Next, as shown in FIG. 22A, the release film 12 a on the heavyreleasability side of the resin film 12 s is released.

[0156] Next, as shown in FIG. 22B, the surface of the coating film ofthe liquid resin composition 12 r and the surface of the resin film 12 sare adhered to each other by using a pad or a roller, etc.

[0157] After that, in the same way as the above processes shown in FIG.17 and FIG. 18, for example, an ultraviolet ray UV is irradiated fromthe transfer substrate 21 side to cure the resin film 12 s and thecoating film of the liquid resin composition 12 r, the surface of theinterlayer 12 and the transfer substrate 21 are separated on theboundary surface, the second optical recording film 13 is formed on theinterlayer 12, and a light transmitting protective layer 14 is formedthereon.

[0158] From the above, an optical disk having a plurality of opticalrecording layers can be produced.

[0159] Also according to this method, by making a thickness of coatingby spin-coat thin to five times as much as the film thicknessirregularity and forming the rest of the thickness with the ultravioletcuring resin film, an interlayer having a little thickness irregularitycan be formed. For example, when forming an interlayer of 20 μm, byapplying a liquid resin of an amount of 5 μm and composing the restamount of 15 μm with an ultraviolet curing resin film, total filmthickness irregularity can be suppressed to ±1 μm or less.

[0160] Other than the above respective production methods, a liquidresin may be respectively applied to the disk substrate side and thetransfer substrate side by performing spin-coating, and the two may beadhered to each other by providing a resin film between them.

[0161] In the above respective methods, the ultraviolet curing may beperformed at a time after adhering to each other or may be performedsuccessively.

[0162] It becomes a multilayer configuration also in this case, so thateffects of improving properties of adhesiveness, releasability andtransferability, etc. can be expected in addition to the film thicknessin the same way as in the case of using the above stacked resin film.

[0163] [Third Embodiment]

[0164] A method of transferring with pressure by using a plasticsubstrate as the transfer substrate in the above first and secondembodiments will be explained.

[0165]FIG. 23 is a partial sectional view showing the schematicconfiguration of a substrate sub, such as a disk substrate formed byinjection molding.

[0166] Generally, when forming a disk substrate by injection molding,the temperature becomes low at the outermost circumferential portion ofthe mold at the time of the injection molding, so that the substrate subhas trumpet-shaped bulge at the outermost circumference. The width isnormally 2 to 3 mm and the height h is several μm to several tens of μm,which depend on an injection molding device and molding conditions.

[0167] Due to this shape, a clearance is liable to arise when adheringthe disk substrate and the transfer substrate via an ultraviolet curingresin film.

[0168] Also, when an injection molded substrate is used also on thetransfer substrate side, the trumpet-shape arises on the both sides ofthe disk substrate and the transfer substrate and leads to interference,so that a clearance is furthermore liable to arise.

[0169] When a clearance arises, it becomes necessary to eliminate orreduce it by defoaming by pressure under a high pressure (for example, 5kg/cm² or more) for several seconds to several minutes and the processesbecome complicated.

[0170] Here, as shown in FIG. 24, when using the injection moldedsubstrate on the transfer substrate 21 side, by making a size of thetransfer substrate 21 larger by an amount of Δø than that of the disksubstrate 10, interference of the trumpet shapes of the disk substrateand the transfer substrate can be reduced and generating clearances canbe reduced.

[0171] Also, by making a size on the transfer substrate side large,there arises an advantage that it can be used as a holding portion atthe time of releasing.

[0172] Also, by lowering rigidity of the transfer substrate, thetransfer substrate can follow the trumpet shape of the outercircumferential portion of the disk substrate and clearances generatedbetween the disk substrate and the transfer substrate can be reduced.

[0173] There is also a method of using a plastic material having a lowrigidity, but it can be improved by simply making the thickness, forexample, to 0.5 mm or less. The thinner, the less clearance arises, butwhen it is too thin, such as thinner than 0.3 mm, injection moldingbecomes difficult and handling becomes difficult.

[0174] Also, by making only the trumpet-shaped outermost circumferentialportion 21 e of the transfer substrate 21 thin to be a taper shape asshown in FIG. 25A, or by making only the trumpet-shaped outermostcircumferential portion 21 e of the transfer substrate 21 shaped to havea step as shown in FIG. 25B, and making the outer circumferentialportion 21 e of the transfer substrate 21 follow the trumpet shape ofthe outer circumferential portion 10 e of the disk substrate 10, aclearance generated between the disk substrate and the transfersubstrate can be reduced.

[0175] For example, a thickness t₁ at the center of the transfersubstrate 21 is assumed to be 0.3 mm or so and a thickness t₂ of theoutermost circumferential thin portion is 0.1 mm or so.

[0176] When the thickness of the transfer substrate 21 is made thin, amaterial composing the transfer substrate is required less, so it isadvantageous in terms of costs.

[0177] Also, when the outermost circumferential portion 21 e of thetransfer substrate 21 is made to be a taper shape or a step shape, it isalso possible to make only the outer circumferential portion thin andthe center portion can be made thick to an extent of. not causing anytroubles in carrying and handling, which are advantageous.

[0178] Also, as a method of bonding with pressure, it is preferable touse an elastic body capable of adhering even a taper shape and a stepshape with pressure, so that the transfer substrate easily follows alongthe trumpet shape of the disk substrate. On the other hand, the disk isplaced on a flat stage so as not to cause any warps, and the transfersubstrate is put above to be adhered with pressure by a pad or a roller.A material of the pad and the roller, rubber can be used but may be anyas far as it has elasticity. A pad shape to be used is flat, circularcone and spindle shape. An adhesive force can be changed in accordancewith rubber hardness and adhesion strokes.

[0179] When using a thin transfer material or a taper shaped transfermaterial, it becomes significant that the optical disk substrate isplaced on a flat stage and the transfer material able to be deformed ispressed with an elastic body.

[0180] Also, methods of making the outer circumference diameter size ofthe transfer material large, using a thin substrate, or making only anouter circumference thin may be used in combination.

EXAMPLE 1

[0181] An ultraviolet curing resin film was produced as below.

[0182] As an ultraviolet curing adhesive, 100 parts by weight of anultraviolet curing resin composed of urethane acrylate based oligomer, 5parts by weight of a photo-polymerization initiator and 5 parts byweight of isocyanate based curing agent were blended with respect to 100parts by weight of an acryl adhesive composed of a copolymer of n-butylacrylate and acrylic acid. The result was diluted with a solvent andapplied on a release film by a roll-coater while mixing. As the releasefilm, a PET (polyethylene terephthalate) film having a thickness of 38μm subjected to silicone processing was used. A base material wasobtained by laminating a PET (polyethylene terephthalate) film having athickness of 38 μm wherein adhesiveness is made light after drying. Thecoater was adjusted so that the thickness becomes 20 μm after drying.

[0183] A multilayer optical disk was produced by using the aboveultraviolet curing resin film as explained below.

[0184] A polycarbonate resin substrate having an outer circumferencediameter ø of 120 mm, inner circumference diameter ø of 15 mm and athickness of 1.1 mm formed with a relief pattern made by a pit on oneside was used. Aluminum was formed thereon to 60 nm by sputtering and afirst optical recording layer was formed.

[0185] Next, the above ultraviolet curing resin film is stamped out tobe a donut shape having an outer circumference diameter ø of 119 mm andinner circumference diameter ø of 23 mm and adhered to the disksubstrate by a roller after removing a release film on the lightreleasability side.

[0186] As a transfer substrate, an injection molded substrate having athickness of 1.1 mm, an outer circumference diameter ø of 120 mm andinner circumference diameter ø of 15 mm composed of a cyclic polyolefinresin was used. The transfer substrate is formed with an uneven shapemade by a pit for a second optical recording layer.

[0187] Next, the disk substrate is placed on a flat metal stage, the PETrelease film on the heavy releasability side was removed, then, thetransfer substrate was bonded with pressure from above by a pad. As thepad, a spindle type rubber pad was used and a pressure was applied untilallover the disk is pressed. The pressing force at the time was 5kg/cm². After the bonding with pressure, the disk was subjected todefoaming processing by being placed under a pressure of 5 to 10 atmsfor 1 second to 5 minutes.

[0188] The ultraviolet curing resin film was cured by irradiating anultraviolet ray from the transfer substrate, and the transfer substratewas released.

[0189] Next, aluminum is formed to be a film to have a film thickness of9 nm by sputtering so as to be translucent, and the second opticalrecording layer was formed.

[0190] As a material of a light transmittance protective layer, the onelaminated with a polycarbonate resin film having a thickness of 60 μmand an adhesive having a thickness of 20 μm in advance, and adhered withthe PET (polyethylene terephthalate) release film on the adhesive sidewas used. The base material was stamped out to be a donut shape havingan outer circumference diameter ø of 119 mm and inner circumferencediameter ø of 23 mm, then, pressed by a spindle shaped pad and adhered.Furthermore, defoaming processing was performed by leaving the diskunder a pressure of 5 to 10 atms for 1 second to 5 minutes.

[0191] An average thickness and thickness unevenness of the protectivelayer and interlayer of an optical disk produced as above were measuredby a spectral interference method (the device name: ETA-Optik made bySteag Co.).

[0192] The measurement was made for every 2 mm from 24 to 56 mm on thedisk radius and every 6 degrees in the circumferential direction of thedisk. The result is shown. From this, it was confirmed that thicknessirregularity of the interlayer of ±1 μm or less was realized. TABLE 1Average Measurement Thickness Maximum Thickness Place (μm) Irregularity(±μm) Interlayer 19.6 0.45 Protective Layer 80.2 0.52 Interlayer + 99.81.06 Protective Layer

EXAMPLE 2

[0193] Two kinds of ultraviolet curing multilayer resin films wereproduced as below.

[0194] As an ultraviolet curing resin film (A) having weak adhesivenessto a polycarbonate resin, a copolymer having a weight-average molecularweight of 300000 composed of n-butyl acrylate and 2-hydroxy ethylacrylate, a photo-curing copolymer obtained by reacting methacryloyloxyethyl isocyanate with ethyl acetate solution, a copolymer having aweight-average molecular weight of 300000 composed of n-butyl acrylateand 2-hydroxy ethyl acrylate and a isocyanate based photopolymerizationinitiator are blended, and what obtained by applying the result in theabove explained method, so that a thickness after drying becomes 10 μmwas used.

[0195] Also, since a polycarbonate resin is used as a disk substrate, asan ultraviolet curing resin film (B) on the adhering side, 100 parts byweight of an ultraviolet curing resin composed of urethane acrylatebased oligomer, 5 parts by weight of a photo-polymerization initiatorand 5 parts by weight of isocyanate based curing agent were blended withrespect to 100 parts by weight of an acryl based adhesive composed of acopolymer of n-butyl acrylate and acrylic acid, and what obtained byapplying the result in the above explained method, so that the thicknessafter drying becomes 10 μm was used.

[0196] First, as a disk substrate, a polycarbonate resin substratehaving an outer circumference diameter ø of 120 mm, inner circumferencediameter ø of 15 mm and a thickness of 1.1 mm formed with an unevenshape made by a pit on one side was used. Aluminum film was formedthereon to be 60 nm by sputtering and a first optical recording layerwas formed.

[0197] Next, the above ultraviolet curing resin film (B) was stamped outto be a donut shape having an outer circumference diameter ø of 119 mmand inner circumference diameter ø of 23 mm and adhered to the disksubstrate by a roller after removing a release film on the lightreleasability side.

[0198] As a transfer substrate, a polycarbonate resin substrate havingan outer circumference diameter ø of 120 mm, inner circumferencediameter ø of 15 mm, and a thickness of 1.1 mm formed with an unevenshape to be a pit on one side was used. The ultraviolet curing resinfilm (A) was stamped out to be a donut shape having an outercircumference diameter ø of 119 mm and an inner circumference diameter øof 23 mm and adhered thereon by a roller after removing a release filmon the light releasability side. After removing both of the releasefilms on the disk substrate and transfer substrate, the result waspressed by a spindle shaped pad to be adhered.

[0199] Furthermore, after performing defoaming processing by leavingunder a pressure of 5 to 10 atms for 1 second to 5 minutes or so, anultraviolet ray was irradiated from the transfer substrate side, and theultraviolet curing films (A) and (B) were cured at a time.

[0200] Next, when separating the transfer material from the optical disksubstrate, the releasing was always performed on the boundary of theultraviolet curing resin film (A) and the transfer substrate.

[0201] After that, an aluminum film was formed by sputtering so as to bea translucent and a second optical recording layer was formed.

[0202] Finally, a light transmitting protective layer was produced inthe same way as in the above method, and a multilayer optical disk wasobtained.

[0203] An average thickness and thickness irregularity of the protectivelayer and interlayer of the optical disk produced as above were measuredon this disk by a. spectral interference method in the same way.

[0204] From this, it was confirmed that thickness irregularity of theinterlayer of ±1 μm or less was attained even when the interlayerconfiguration became two layers. TABLE 2 Average Measurement ThicknessMaximum Thickness Place (μm) Irregularity (±μm) Interlayer 19.6 0.78Protective Layer 80.3 0.46 Interlayer + 99.9 1.20 Protective Layer

EXAMPLE 3

[0205] A multilayer disk wherein an interlayer was composed of a resinfilm of an ultraviolet curing adhesive and an ultraviolet curing resinapplied with. spin-coating was produced as below.

[0206] An ultraviolet curing adhesive was used as the ultraviolet curingresin film. What obtained by blending 100 parts by weight of anultraviolet curing resin made by urethane acrylate based oligomer, 5parts by weight of photo-polymerization initiator and 5 parts by weightof an isocyanate based curing agent with respect to 100 parts by weightof acryl based adhesive composed of a copolymer of n-butyl acrylate andacrylic acid is applied to be a thickness of 17 μm in the aboveexplained method.

[0207] As an optical disk substrate, a polycarbonate resin substratehaving an outer circumference diameter ø of 120 mm, inner circumferencediameter ø of 15 mm, and a thickness of 1.1 mm formed with an unevenshape to be a pit on one side was used. An aluminum film was formed tohave a film thickness of 60 nm by sputtering thereon so as to form afirst optical recording layer.

[0208] Next, the ultraviolet curing resin film was stamped out to be adonut shape having an outer circumference diameter ø of 119 mm and innercircumference diameter ø of 23 mm and adhered to the disk substrate by aroller after removing a release film on the light releasability side.

[0209] As a transfer substrate, an injection molded substrate made by acyclic polyolefin resin having a thickness of 1.1 mm, an outercircumference diameter ø of 120 mm and an inner circumference diameter øof 15 mm was used. The transfer substrate was formed with an unevenshape to be a pit for a second optical recording layer.

[0210] On the surface of the transfer substrate is applied with an acrylbased ultraviolet curing resin (for example, T-695/UR506-4 made byNagase Chiba) in a pattern of a ring shape at a position of a radius of10 to 20 mm and spin-coating was performed. The rotation rate was 5000rpm and the rotation time was adjusted so that the thickness at theoutermost circumference becomes 3 μm.

[0211] Next, an optical disk substrate is placed on a flat metal stage,and after removing a PET release film on the heavy releasability side,the transfer substrate provided with a coating film of an ultravioletcuring resin was adhered with pressure from above by a pad. Furthermore,after performing defoaming processing by leaving under a pressure of 5to 10 atms for 1 second to 5 minutes or so, an ultraviolet ray wasirradiated from the transfer substrate side to cure the ultravioletcuring resin film and the ultraviolet curing resin coating film at atime.

[0212] After that, an aluminum film was formed by sputtering so as to betranslucent and a second optical recording film was formed. Finally, alight transmitting protective layer was prepared in the same way as theabove explained method and a multilayer optical disk was obtained.

[0213] An average thickness and thickness irregularity of the protectivelayer and interlayer of the optical disk produced as above were measuredon the optical disk by a spectral interference method. Also in thiscase, it was possible to make the thickness irregularity of theinterlayer to be ±1 μm or less. TABLE 3 Average Measurement ThicknessMaximum Thickness Place (μm) Irregularity (±μm) Interlayer 19.1 0.89Protective Layer 79.9 0.41 Interlayer + 99.0 1.38 Protective Layer

EXAMPLE 4

[0214] To avoid interference by a trumpet shape at the outercircumferential portion of the transfer substrate, a cyclic polyolefinresin substrate having an outer circumference diameter ø of 128 mm,inner circumference diameter ø of 15 mm, and a thickness of 1.1 mmformed with an uneven shape to be a pit on one side was used as atransfer substrate.

[0215] As a disk substrate, a polycarbonate resin substrate having anouter circumference diameter ø of 120 mm, inner circumference diameter øof 15 mm, and a thickness of 1.1 mm formed with an uneven shape to be apit on one side was used.

[0216] After adhering an ultraviolet curing resin film having athickness of 20 μm on the disk substrate, the disk substrate was placedon a flat metal stage, and after a PET release film on the heavyreleasability side was removed, the transfer substrate was adhered withpressure from above by a pad. As the pad, spindle type rubber pad wasused and pressure was applied until allover the disk was pressed. It wasconfirmed that the thus obtained disk had almost no bubbles left at theouter circumference by performing pressure defoaming.

EXAMPLE 5

[0217] Next, an optical disk was produced in the same way as the aboveby using a transfer substrate wherein the thickness was made thin.

[0218] As the transfer substrate, a cyclic polyolefin resin substratehaving an outer circumference diameter ø of 120 mm, inner circumferencediameter ø of 15 mm, and a thickness of 0.35 mm formed with an unevenshape to be a pit on one side was used.

[0219] As a disk substrate, a polycarbonate resin substrate having anouter circumference diameter ø of 120 mm, inner circumference diameter øof 15 mm, and a thickness of 1.1 mm formed with an uneven shape to be apit on one side was used.

[0220] After adhering an ultraviolet curing resin film having athickness of 20 μm on the disk substrate, the optical disk as a transfersubstrate was placed on a flat metal stage, and after a PET release filmon the heavy releasability side was removed, the transfer substrate wasadhered with pressure from above by a pad.

[0221] As the pad, spindle type rubber pad was used and pressure wasapplied until allover the disk was pressed. It was confirmed that thethus obtained disk had almost no bubbles left at the outer circumferenceby performing pressure defoaming.

EXAMPLE 6

[0222] Next, only a shape of the outermost circumference of the transfersubstrate was made thin. An outer circumference diameter ø was 120 mm,the inner circumference diameter ø was 15 mm, a thickness near thecenter was 0.6 mm, the plate thickness gradually became thinner from theposition of the radius of 45 mm, and the plate thickness at the positionof the radius of 60 mm, the outermost circumference, was 0.2 mm. Thistaper shape was formed on the opposite side of the surface formed withthe uneven shape to be a pit, and a cyclic polyolefin resin was used asa transfer substrate material.

[0223] The disk substrate had an outer circumference diameter ø of 120mm, inner circumference diameter ø of 15 mm, and a thickness of 1.1 mmand an uneven shape made by a pit formed on its one side.

[0224] After adhering an ultraviolet curing resin film having athickness of 20 μm on the disk substrate, the optical disk as a transfersubstrate was placed on a flat metal stage, and after a PET release filmon the heavy releasability side was removed, the transfer substrate wasadhered with pressure from above by a pad.

[0225] As the pad, spindle type rubber pad was used and pressure wasapplied until allover the disk was pressed. It was confirmed that thethus obtained disk had almost no bubbles left at the outer circumferenceby performing pressure defoaming.

[0226] According to the multilayer optical disk and the productionmethod of the present embodiment, advantages below can be obtained.

[0227] By using an ultraviolet curing resin film as the interlayer, filmthickness irregularity of the interlayer can be suppressed small, sothat a multilayer disk capable of stably recording and reproducing canbe provided.

[0228] By using an ultraviolet curing resin film as the interlayer, filmthickness irregularity of the interlayer can be suppressed small, sothat a multilayer optical disk having two or more optical recordinglayers can be provided.

[0229] By forming the interlayer by two or more kinds of ultravioletcuring resin films, a wide range of materials can be used as a materialof the transfer substrate.

[0230] By forming the interlayer by two or more kinds of ultravioletcuring resin films, an interlayer having good transferability and asuppressed shrinking percentage can be provided.

[0231] By combining an ultraviolet curing resin coating film, whereinthe thickness is made thinner than that in the case of being used alone,and an ultraviolet curing resin film, film thickness irregularity of theinterlayer. can be suppressed and the same effects can be obtained as inthe case of using two or more layers of ultraviolet curing resin films.

[0232] When using a substrate made by an injection molded plasticmaterial as the transfer substrate, preferable transfer can be performedby making the outer circumference diameter of the transfer substratelarger than that of the optical disk substrate.

[0233] When using a transfer substrate made by a plastic material, goodtransferability can be obtained to the outer circumference by making thethickness of the transfer substrate to as thin as 0.5 mm or less.

[0234] When using a transfer substrate made by a plastic material, goodtransferability can be obtained to the outer circumference by making theoutermost circumferential portion of the transfer substrate thin.

[0235] Also, other than being able to suppress the film thicknessirregularity of the interlayer as explained above, the influence ofwarps of the transfer substrate, arising of problems due to dusts andburrs can be also suppressed by using an ultraviolet curing resin filmas the interlayer.

[0236] The present invention is not limited to the above embodiments.

[0237] For example, as the optical recording layer, other than areflection film of aluminum, etc., other variety of optical recordinglayers of a phase change type recording material, etc. can be used.

[0238] Also, it can be applied to an optical recording medium havingthree or more optical recording layers.

[0239] Other than the above, a variety of modifications can be madewithin the scope of the present invention.

[0240] According to the present invention, a plurality of opticalrecording layers are provided, wherein film thickness irregularity ofinterlayer between the optical recording layers can be suppressed,furthermore, the influence of warps of the transfer substrate, arisingof problems due to dusts and burrs can be also suppressed.

Industrial Applicability

[0241] The present invention can deal with memory formats of arewritable type, etc. having an optical recording layer using as arecording material a phase change type material, magneto-opticalrecording material or recording material containing organic dye, etc.and can be used for an optical disk capable of realizing a largecapacity file at a low cost and the production method thereof.

1. An optical recording medium, wherein at least two optical recordinglayers stacked via an interlayer and a light transmitting layer providedon the optical recording layer are provided at least one surface of amedium substrate, for performing recording and reproducing byirradiating a light to said optical recording layer through the lighttransmitting layer; and said interlayer includes at least one layer ofultraviolet curing resin film made to be a film in advance and is a filmformed with an uneven shape corresponding to a recording pit or anuneven shape to be a guide groove on its surface and cured.
 2. Anoptical recording medium as set forth in claim 1, wherein saidinterlayer is a film obtained by curing a stacked structure including atleast one layer of ultraviolet curing resin film made to be a film inadvance and at least one layer of a coating film of an ultravioletcuring liquid resin composition.
 3. An optical recording medium as setforth in claim 1, wherein an uneven shape corresponding to a recordingpit or an uneven shape to be a guide groove on the surface of said resinfilm in said interlayer.
 4. An optical recording medium as set forth inclaim 2, wherein an uneven shape corresponding to a recording pit or anuneven shape to be a guide groove on the surface of said coating film ofan ultraviolet curing liquid resin composition.
 5. A method of producingan optical recording medium having at least two optical recordinglayers, including a step of forming a medium substrate having an unevenshape on its one surface, a step of forming a first optical recordinglayer on the uneven shape formation surface of said medium substrate, astep of forming an interlayer having an uneven shape on its surface onsaid first optical recording layer, a step of forming a second opticalrecording layer on the uneven shape formation surface of saidinterlayer, and a step of forming a light transmitting protective layeron said second optical recording layer; wherein the step of forming saidinterlayer includes a step of adhering one surface of an ultravioletcuring resin film made to be a film in advance to said first opticalrecording layer or a transfer substrate formed with an uneven shape, astep of pressing said transfer substrate or said first optical recordinglayer directly or via other layer against said resin film and providingan uncured interlayer including at least one layer of said resin filmbetween said first optical recording layer and said transfer substrate,a step of curing said interlayer in a state of pressing said transfersubstrate against the surface of said interlayer, and a step ofreleasing said transfer substrate from said interlayer and transferringthe uneven shape of said transfer substrate to the surface of saidinterlayer.
 6. A method of producing an optical recording medium as setforth in claim 5, wherein: said resin film is an ultraviolet curingresin film made to be a film in a state of being sandwiched by a pair ofrelease films; and the step of forming said interlayer further includesa step of releasing one of said release films from said resin filmbefore the step of adhering said resin film to said first opticalrecording layer or said transfer substrate, and a step of releasing theother of said release films from said resin film after the step ofadhering said resin film to said first optical recording layer or saidtransfer substrate and before the step of pressing said transfersubstrate or said first optical recording layer directly or via otherlayer against said resin film.
 7. A method of producing an opticalrecording medium as set forth in claim 5, wherein said interlayer isformed only with said resin film in the step of forming said interlayer.8. A method of producing an optical recording medium as set forth inclaim 5, wherein the step of forming said interlayer includes a step ofadhering said resin film on said transfer substrate, a step of forming acoating film of an ultraviolet curing liquid resin composition on saidfirst optical recording layer, a step of adhering said resin film andsaid coating film, a step of obtaining said interlayer by curing saidresin film and said coating film in a state of being adhered to eachother, and a step of releasing said transfer substrate from saidinterlayer.
 9. A method of producing an optical recording medium as setforth in claim 5, wherein the step of forming said interlayer includes astep of forming a coating film of an ultraviolet curing liquid resincomposition on said transfer substrate, a step of adhering said resinfilm on said first optical recording layer, a step of adhering saidresin film and said coating film, a step of obtaining said interlayer bycuring said resin film and said coating film in a state of being adheredto each other, and a step of releasing said transfer substrate from saidinterlayer.
 10. A method of producing an optical recording medium as setforth in claim 5, wherein one made by an injection molded plasticmaterial having a larger outer circumference diameter than that of saidmedium substrate is used as said transfer substrate.
 11. A method ofproducing an optical recording medium as set forth in claim 5, whereinone made by a plastic material having a thickness of 0.5 mm or less isused as said transfer substrate.
 12. A method of producing an opticalrecording medium as set forth in claim 5, wherein one made by a plasticmaterial wherein the outer circumference diameter is taper shaped andthinner than the center portion is used as said transfer substrate. 13.A method of producing an optical recording medium as set forth in claim5, wherein adhesion with pressure is performed from the transfersubstrate side by an elastic body in the step of transferring by usingsaid transfer substrate.